Telephone instrument



ll Other objects of this invention will be matic and partially 6 govided with a depending flange 7.

Patented Aug. 28, 1928.

1,682,505 PATENT OFFICE.

CLINTON R; HANNA, OF WI ILK INSBURG, PENNSYLVANIA, ASSIGNOR 'IYO WESTING- HOU VANIA.

Application filed August 28,1924.

5 type in which the diaphragm is maintained under tension between two magnetic devices. ne object of this invention is to produce a telephonic device which will have a better response to currents of high frequency.

A*further object of this invention is to provide means by which a thinner diaphragm may be used than has heretofore been possible Without introducing instability.

Another object of this invention is to pro 15 vide means by which a thin diaphragm may be used in telephone devices having much stronger constant magnetic fields than have hertofore been used.

A further object of this invention is to so provide means by which the resonance frequencies above the fundamental may be moved beyond the range of audibility, without greatly increasing the frequency of the fundamental.

apparent from the following description, when read drawing, wherein:

Figure 1 is a view, partially diagramin section, illustrating one form ofmy invention,

Fig. 2 is a similar view 011a modification.

The diaphragm l is of magnetic material,

such as mild steel. Any convenient means maybe employed for maintaining the diaphra m under tension. The means chosen for ilustration include two rings '3 and fl threaded together. .The diaphragm 1' 1S clamped between the rings 3 and The. ring 3 is provided with a flange 5 which projects above the clamping surface. The inner surface of the ring 4:, above the clamping iace,'is threaded to receive a threaded ring y screwing the ring 6 into the ring 4, the flange 7 may be made to depress the dia phragm 1 below the upper edge of the flange 5. The extent of this depression regulates the degree of tension. The tension may, therefore, be adjusted by screwing the ring 6 into or out of the ring 4.

A 8 is situated on one side of the diaphragm 1 and a magnet 9 upon the opposite side.

In connection with the accompanying tween the poles of one and a diaphragm,

These may be either permanent or ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- rnnnrnoun INSTRUMENT.

Serial No. 734,60.

electromagnets or permament magnets reinforced by magnetizing coils. The coil 11 up'on magnet 8 and the coil 12 upon the magnet are connected in series through a source of direct current 13 and a rheostat orother regulating device 14. The direction of'magnetization in the permanent magnets or the direction of current through the coils 11 and 12 is such that the north pole of the magnet 8 is opposite the south pole of the magnet 9.

onsequently, the north pole of the ma 9 is opposite the south pole of the magnet 8 Winding the magnet 8 and a winding 17 upon a magnet 9, are connected inseries, the connection including the ter-. minals 18 by which the signalling current is introduced into the instrument. The direction of the windings16 and 17 is such that, when the fiux due to the magnet 8 is increased by the flux due to the current in the winding 16, the flux in the magnet 9 is decreased b the fiuxdue to the current in the winding 1 and vice versa. i p

In the form shown in Fig. 2, andinductor 20 is connected across the terminals 18." The source 13 and the rheostat let are connected to the center of the inductor 20 and to the the current due to the battery 13 produces in the magnet 8 a north pole opposite the south 'pole which it produces in the magnet 9 and a north pole in the magnet 9 opposite the south pole which it produces in the ma net 8. The signalling current, on the other hand, will strengthen the magnet 8 when it is in the direction to Weaken the magnet 9 and vice versa.

hen no signalling current is being received, the diaphragm 1 is in equilibrium be.- the magnets. Moreover, the magnetic potential of the part of the diaphragm between the two right-hand poles isthe same as that of the part between the two left-hand poles. Consequently, the diaphragm carries little or no fiux. For this reason, the diaphragm need not be thick and, therefore, need 'not be heavy.

A thin diaphragm is less rigid than a thick the thickness of which is only suflicient to carry, without saturation, the small flux required by the arrangement just described, would not-be sufficiently rigid to be stable. 7

gnet- I this change has the proper p By turning the ring 6 so increases the tension upon the diaphragm, a force, due to the elasticity of the diaphragm and tending to restore it to its mid-position when it is displaced, is introduced. This force is in the same direction and of the same phase as the force due to the stiffness of the ,diaphragm. Stretching the diaphragm by means of the ring 6 is, therefore, equivalent to increasing the rigidity thereof.

When the diaphragm is displaced upward, it is nearer to the poles of the magnet 8. The attraction between the diaphragm and this magnet is, it the that the flange 7 therefore, increased. 1 same time the diaphragm is more remote from the magnet 9, and the attraction by this mag net is diminished. The forces due to the two magnets do not balance, therefore, when the diaphragm is displaced. The difference between these forces is in phase with the displacement and in a direction to increase such displacement. Its effect, therefore, is to counteract the reaction due to the rigidity of the 'dia hragm.

onsequently, of the magnets, we may stretched diaphragm, the effect of a diminution in rigidity. Although the explanation of this effect of the magnets on the aparent rigidity has been made in connection with a diaphragm between two magnets, the effect is also obtained when but one magnet is present, because, even in that case, a displacement of the diaphragm tends to produce a change in the magnetic attraction an hase to tend to counteract the rigidity of the diaphragm.

At certain frequencies, the diaphragm vibrates more in response to the same degree of stimulus than at others. The lowest of these we call the fundamental and the higher ones harmonics although they are not necessarily related in any simple way to the fundamenta Upon stretching the diaphragm the frequency, both for the fundamental and for the harmonics, is increased. The increase in the frequency of the fundamental is not as great as the increase in the frequencies of the several higher resonance periods.

The harmonics are due to a motion of the diaphragm in which it vibrates in a more or less complex fashion. The linear displacement ofthe diaphragm during such complex vibration is less than for the fundamental. Consequently, the tendency of the magnetic field to counteract the effect of the rigidity due to the stretching is less for the harmonics than for the fundamental.

By counteractin the effect of rigidity, the magnetic field ten 5 to reduce the resonance frequency. The diminution in the frequency corresponding to the fundamental, noticed when the magnetic field is increased is greater by increasing the strength produce, in the.

than the corresponding diminution in the frequencies of the harmonics. It is, therefore, possible, by properly relating the tension of the diaphragm and the magnitude of the magnetic field, to have all of the harmonics above the range of audibility and the fundan'iental not much above its original pitch. This relation may be secured by the design of the instrument or by providing for the adjustment of the constant flux. Such an adjustment is indicated by adjustment of the position of one or both magnets to vary the air gap would produce the same result.

This leaves thofundamental as the only resonance point within the audible range. The circuit with which the instrument is used may be so designed that the resonance of the instrument at one frequency may be corrected by the resonanceof the circuit.

Because this structure enables one to use a diaphragm of smaller mass than has hitherto been possible, the reaction due to inertia is diminished.

effective at the higherfrequencies. The diminution in it. therefore, renders the instrument more effective for high notes.

Although I have illustrated and specifically described but one modification of my invention, it will be apparent to those skilled in the art that many applications thereof are possible. I do not, therefore, intend the specific description to be construed as a limitation. No limitation except that required by the prior art or expressed by the claims is intended.

I claim as my invention:

1. In a telephone instrument, a diaphragm, means for maintaining said diaphragm under tension, said tension being sufficient to bring a resonance frequency of the harmonics of said diaphragm above the range of audibility and magnetic means for counter-acting the effect of said tension upon the fundamental frequency of said diaphragm.

2. In a sound-reproducing apparatus a diaphragm, means for mounting said diaphragm under tension to increase the effective stiffness thereof, magnetic means for producing a displacing effect on said diaphragm which increases with displacement thereof, said tensioning means being so proortioned to said magnetic means that the effect of one. upon the fundamental natural period of the diaphragm nearly counterbalances the effect of the other but said effects upon the harmonic natural periods of said diaphragm raise them above the intended range 0 the apparatus.

In testimony whereof I have hereunto subscribed my name this 22nd day of August,

CLINTON R. HANNA.

the adjustable rheostat 14. An

This reaction is particularly 

